1. Field of the Invention
The present invenion relates to novel organometallic compounds and, more particularly, to novel polymeric organoaluminum hydrocarbyl compounds in which at least one valence of the metal is satisfied by a low density polyethylene radical. The invention further relates to Ziegler-Natta type catalysts systems comprising a transition metal compound, an organometallic catalyst and the novel organoaluminum compounds containing the low density polyethylene radical. The invention also relates to polyethylenes obtained by polymerizing ethylene in the presence of the catalyst system.
It is well known that the molecular weight and long chain branching of polyethylene are factors affecting die swell during the extrusion of the polyethylene to form polymeric articles. Excessive die swell may result in overweight parts, high head pressure, excessive flashing and parison stability problems; insufficient swell may result in underweight parts, nonuniform wall thickness as well as other related problems. Although die swell can be controlled by controlling the shear rate during extrusion, it would be advantageous to control die swell through modification of the polymer to be extruded.
Accordingly, it would be desirable to produce a polymer composition which would evidence suitable die swell at for example a shear rate of 300 sec.sup.-1.
2. Description of the Prior Art
In U.S. Pat. No. 3,149,136 there is described organometallic aluminum compounds wherein the repeating units contain an aluminum atom. The polymeric compounds are produced by contacting a diene, such as isoprene, with an aluminum trialkyl, for example aluminum triisobutyl.
In British Pat. No. 1,333,098 there is described a process for the production of polymeric organoaluminum compounds by contacting a dialkylaluminum hydride such as diisobutylaluminum hydride with isoprene. The alkyl aluminum polymers are employed in combination with transition metal halides to form a catalyst system for the polymerization of mono-olefins and diolefins and for copolymerizing two or more such olefins.
British Pat. No. 901,148 teaches a method of producing branched polyethylene from linear polyethylene by treatment of the polyethylene melt with oxygen at 160.degree. to about 280.degree. C. An objective of the invention described in the patent is the conversion of high density polyethylene to low density polyethylene.
In British Pat. No. 1,379,853 it is taught that the flow properties of molten polymers are improved by introducing small amounts of long chain branches into high density linear polyethylene. The introduction of the long chain branches is accomplished without affecting rigidity and density. The patentees accomplish the introduction by reacting high density polyethylene with about 0.05 to 10 weight percent of peroxides based on the polyethylene.
It would be highly desirable to be able to introduce small amounts of long chain branches into the linear polyethylene during the catalytic polymerization of ethylene to polyethylene thereby avoiding the additional steps required in modification of linear polyethylene by chemical reaction.